diff --git a/metafix/src/test/java/org/metafacture/metafix/MetafixMethodTest.java b/metafix/src/test/java/org/metafacture/metafix/MetafixMethodTest.java
index 9f58ecce..8a8b230e 100644
--- a/metafix/src/test/java/org/metafacture/metafix/MetafixMethodTest.java
+++ b/metafix/src/test/java/org/metafacture/metafix/MetafixMethodTest.java
@@ -19,9 +19,11 @@
 import org.metafacture.framework.StreamReceiver;
 
 import com.google.common.collect.ImmutableMap;
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.Mock;
+import org.mockito.exceptions.base.MockitoAssertionError;
 import org.mockito.junit.jupiter.MockitoExtension;
 
 import java.util.Arrays;
@@ -36,6 +38,9 @@
 @ExtendWith(MetafixToDo.Extension.class)
 public class MetafixMethodTest {
 
+    private static final String YOUTUBE_URL = "https://www.youtube.com/watch?v=daLgsPSvD9A";
+
+    private static final String YOUTUBE_URL_AS_URL_URL_BASE64 = "aHR0cHM6Ly93d3cueW91dHViZS5jb20vd2F0Y2g_dj1kYUxnc1BTdkQ5QQ==";
     @Mock
     private StreamReceiver streamReceiver;
 
@@ -4086,20 +4091,31 @@ public void shouldTransformStringToBase64() {
 
     @Test
     public void shouldTransformUrlToBase64() {
+        urlToBase64(",url_safe:'true'");
+    }
+
+    @Test
+    public void shouldFailTransformUrlToBase64AsDefault() {
+        Assertions.assertThrows(MockitoAssertionError.class, () -> {
+            urlToBase64("");
+        });
+    }
+
+    private void urlToBase64(final String option) {
         MetafixTestHelpers.assertFix(streamReceiver, Arrays.asList(
-                "to_base64('data.title', url_safe:'true')"
+                "to_base64('data.title'" + option + ")"
             ),
             i -> {
                 i.startRecord("1");
                 i.startEntity("data");
-                i.literal("title", "https://www.youtube.com/watch?v=daLgsPSvD9A");
+                i.literal("title", YOUTUBE_URL);
                 i.endEntity();
                 i.endRecord();
             },
             o -> {
                 o.get().startRecord("1");
                 o.get().startEntity("data");
-                o.get().literal("title", "aHR0cHM6Ly93d3cueW91dHViZS5jb20vd2F0Y2g_dj1kYUxnc1BTdkQ5QQ==");
+                o.get().literal("title", YOUTUBE_URL_AS_URL_URL_BASE64);
                 o.get().endEntity();
                 o.get().endRecord();
             }